The present invention generally relates to the joining of ocular tissues, and more particularly to the welding of ocular tissues (e.g. scleral and corneal tissues) to each other using laser light in a manner which avoids disfigurement and/or destruction of the tissues.
In recent years, many advances have been made in the medical use of laser technology. Techniques involving the application of laser light have proven to be beneficial in many medical fields ranging from cardiology to ophthalmology. For example, substantial developments have been made using laser energy for the welding of blood vessels, arteries, and the like. The laser welding of vascular tissues is discussed in Jain, K. K. et al., "Repair of small blood vessels with the Neodymium-YAG laser: A preliminary report", Surgery, 85(6):684-688 (1979). This article provides a general discussion of laser surgical techniques and the advantages thereof. Other articles which discuss the laser welding of vascular tissues include Vance, C. A. et al., "Laser Assisted Vessel Anastomosis of Coronary Arteries in Vitro: Optimization of Bonding Conditions", Lasers in Medical Science, 3:219-227 (1988); Schober, R., et al., "Laser-Induced Alteration of Collagen Substructure Allows Microsurgical Tissue Welding", Science, 232:1421-1422 (1986); White. R. A., "Technical frontiers for the vascular surgeon: Laser anastomotic welding and angioscopy-assisted intraluminal instrumentation", Symposium: Vascular Applications of Angioscopy and Lasers, Journal of Vascular Surgery, 5(4):673-680 (1987); Chuck, R. S., et al., "Dye-Enhanced Laser Tissue Welding", Lasers in Surgery and Medicine, 9:471-477 (1989); White, R. A., "Argon laser-welded arteriovenous anastomoses", Journal of Vascular Surgery, 6(5) 447-453 (1987); and Jain, K. K., "Sutureless Microvascular Anastomosis Using a Neodymium-YAG Laser", Journal of Microsurgery, 1:436-439 (1980). All of the foregoing articles discuss vascular welding experiments involving the use of carbon dioxide lasers (wavelength=10,600 nm), argon lasers (wavelength=488 and 514 nm), or Nd:YAG lasers (wavelength=1064 and 1319 nm).
A number of U.S. Patents also exist which involve the sealing/welding of vascular and other tissues using laser energy. These patents include U.S. Pat. No. 4,917,084 to Sinofsky (laser repair of artery walls and the removal of atherosclerotic plaque using laser energy having a wavelength of 1400-2200 nm); U.S. Pat. No. 4,929,246 to Sinofsky (laser welding of arteries using a laser wavelength of 1400-2500 nm); U.S. Pat. No. 4,892,098 to Sauer (laser welding of vascular tissues using Nd:YAG green laser light [wavelength=510 nm]); U.S. Pat. No. 4,633,870 to Sauer (laser welding of tubular tissues using Nd:YAG and/or carbon dioxide laser light); and U.S. Pat. No. 4,672,969 to Dew (wound closure in the following tissues: skin, nerve fiber, vascular tissues, reproductive tissue structures such as vas deferens or fallopian tubes, gastrointestinal tract, eye tissues, and tendons using a monochromatic beam of laser energy having a wavelength of between 1200-1400 nm). Additional information regarding vascular welding using laser technology is further disclosed in Jain, K. K., Handbood of Microsurgery, Charles C. Thomas Co., pp. 37-39 (1983).
Other uses of laser technology are disclosed in U.S. Pat. No. 4,733,660 to Itzkan and U.S. Pat. No. 4,832,004 to Heckele. U.S. Pat. No. 4,733,660 involves the use of laser energy (wavelength=less than 600 nm) for dermatological purposes (e.g. the treatment of hemangioma which is more commonly known as "port wine stain syndrome"). U.S. Pat. No. 4,832,004 discloses a laser laryngoscope which is used in the endoscopic laser treatment of larynx diseases. A wide variety of laser-related medical techniques/equipment are also disclosed in U.S. Pat. No. 4,641,650 to Mok; U.S. Pat. No. 4,736,745 to Gluckman; U.S. Pat. No. 4,800,899 to Eliott; U.S. Pat. No. 4,840,939 to Leveen et al.; U.S. Pat. No. 4,848,339 to Rink et al.; U.S. Pat. No. 4,869,247 to Howard III, et al.; U.S. Pat. No. 4,950,267 to Ishihara et al.; U.S. Pat. No. 4,968,314 to Michaels; and European Patent Specification No. 0327410.
In the area of ophthalmology, a substantial amount of research has been conducted regarding the use of laser light in photocoagulation processes designed to treat a variety of problems, including diabetic retinopathy, retinal tears, glaucoma, and retinal vascular diseases. Various devices designed to implement photocoagulation processes are disclosed in U.S. Pat. No. 3,467,099 to Lotmar; U.S. Pat. No. 3,487,835 to Koester et al.; U.S. Pat. No. 3,547,125 to Tagnon; U.S. Pat. No. 3,930,504 to de Laforcade; U.S. Pat. No. 4,526,170 to Tanner; U.S. Pat. No. 4,537,193 to Tanner; U.S. Pat. No. 4,776,335 to Nakanishi et al.; and U.S. Pat. No. 4,917,486 to Raven et al. These patents disclose the use of a variety of different laser light wavelengths including 418-514 nm (Tanner '193), 800 nm (Raven et al.), and 693 nm (Koester et al.).
Additional research and development in the area of ophthalmology has been reported in a number of other journal articles and patents. For example, U.S. Pat. No. 4,976,709 to Sand discloses the shrinkage of corneal tissues in order to correct vision problems using discrete bursts of laser light having a wavelength of 1800-2550 nm with the applied energy per burst being about 0.01-5.0 joules. Gailitis, R. P., "Laser Welding of Synthetic Epikeratoplasty Lenticules to the Cornea", Refractive and Corneal Surgery, 6:430-436 (1990), and Keates, R. H., "Carbon dioxide laser use in wound sealing and epikeratophakia", J. Cataract Refract. Surg., 13:290-295 (1987) both describe the use of a carbon dioxide laser (wavelength=10,600 nm) for the laser welding of epikeratoplasty lenticules to corneal tissues, with such experiments resulting in detectable tissue damage/shrinkage.
Accordingly, a wide variety of work has been done in the medical field using laser technology. However, a substantial need remains for a method wherein ocular tissues, namely corneal and scleral tissues, may be welded together using laser energy in order to produce a weld which avoids fluid leakage and promotes healing. This is especially important with respect to the cornea which serves as the primary refractive surface for producing visual images in the eye. The human cornea is a tough structure which is transparent and has a central thickness of about 0.54 mm. As described in greater detail below, the cornea forms the anterior boundary of the anterior chamber in the eye which contains the aqueous humor. The aqueous humor consists of a clear, watery fluid that is maintained at a pressure of about 15-22 mm Hg. Leakage of the aqueous humor occurs with any perforation of the cornea. Leakage can also occur after the closure of an incision, such as the circular incision made during a corneal transplant procedure. In addition, corneal wounds which are sutured unevenly or have areas of tissue overlap can cause substantial changes in the curvature of the cornea, thereby producing astigmatism. For example, in cataract surgery, an incision of up to 6.0 mm in length is made in the limbus of the eye which comprises the junction between the cornea and sclera. In this surgical procedure, tissue overlap and/or uneven regions of the incision can occur, again causing astigmatism in a patient. Likewise, in corneal transplant surgery, improper wound healing can cause fluid leakage and optical astigmatism. This is especially true in corneal transplant operations, since the incision is substantial in size, normally involving a round wound having a diameter of about 6-9 mm. Furthermore, if wound healing does not properly occur in a corneal transplant operation, the epithelial tissue of the cornea (described in greater detail below) can grow downwardly along a path between the donor and host tissue, thereby causing a delay in tissue healing.
The sclera is a white structure which is thicker than the cornea (e.g. about 0.6 mm thick) and comprises most of the outer covering of the eye. The junction between the cornea and the sclera is known as the limbus as indicated above. A common operation in the sclera is the formation of a superior incision near the limbus in order to remove the crystalline lens. Since the sclera supports the cornea at the edges, and since the cornea forms a strong lens element to focus light within the eye, any minor change in the support of the cornea by the sclera can cause the cornea to become astigmatic. As a result, this can impart optical astigmatism to the cornea. These problems may be caused by the gaping of an incision which, for example, could occur following cataract surgery. Astigmatic changes can also occur during the process of wound healing as a result of traction exerted by fibroblasts on collagen fibrils during wound healing.
The cornea and sclera are comprised of a stroma primarily consisting of fibrous collagen proteins, surrounded by a matrix comprised of other proteins. However, the cornea and sclera actually consist of about 80% by weight water, the importance of which in regard to laser treatment is described in greater detail below. In contrast, layers of cellular tissue make up no more than about 10% of the thickness of the cornea.
While numerous developments have been made with respect to the joining of other tissues (e.g. vascular tissues), a significant need exists for a laser welding method which enables the joining of ocular tissues (e.g. corneal and scleral tissues) without charring and destructive deformation. The present invention satisfies this need in a unique manner as described in greater detail below.